Enhanced photovoltaic performance of inverted polymer solar cells by incorporating graphene nanosheet/AgNPs nanohybrids

A linear-dendritic block copolymer (LDBC) functionalized exfoliated graphene nanosheets (XGS)/silver nanoparticles (AgNPs) was prepared for using as the interfacial layer between the zinc oxide (ZnO) based electron-selective layer and poly(3-hexylthiophene) (P3HT)/fullerene derivative (PC61BM) blend based photoactive layer in an inverted polymer solar cell (PSC). The LDBCs were prepared by the respective addition reaction of a hydrophilic poly(oxyalkylene)amine with hydrophobic dendrons of various generations based on 4-isocyanate-4′-(3,3-dimethyl-2,4-dioxo-azetidine)-diphenylmethane (IDD). The dendrons having polyurea/malonamide functionalities were synthesized by using IDD as a building block. Moreover, the dendrons comprised not only hydrogen bond-rich malonamide linkages, but long alkyl chains at the peripheries as well. XGS were respectively grafted with these amphiphilic LDBCs to afford XGS-dendritic derivatives (XGS-G0.5, XGS-G1.5, and XGS-G2.5). Subsequently, a nanohybrid, XGS-G2.5/AgNPs was obtained through the reduction of Ag+ on the surface of LDBC modified XGS. The dendrons would serve as the effective templates for hosting AgNPs. By the incorporation of XGS-G2.5/AgNPs nanohybrid, it rendered the PSC an increased power conversion efficient (PCE) to 4.04%, a 19.5% improvement over a PCE of 3.38% for the bare inverted PSC, due to the localized surface plasmon resonance of AgNPs, and the improvement of compatibility and charge transfer capacity between ZnO based cathode and photoactive layer. This journal is © The Royal Society of Chemistry 2015.